Method for surface treatment of nickel and cobalt base alloys

ABSTRACT

The treatment of high nickel and cobalt base alloy to improve the corrosion resistance of parts formed thereof by first applying a coating of nickel and then subjecting the part to diffusion coating to aluminize the surface.

United States Patent Schwartz et al.

[ Feb. 8, 1972 [54] METHOD FOR SURFACE TREATMENT OF NICKEL AND COBALT BASE ALLOYS [72] Inventors: Charles W. Schwartz, Whitehall, Mich;

Richard W. Martini, Scotia, NY.

[73] Assignee: Howmet Corporation, New York, NY.

[22] Filed: Sept. 8, 1969 [21] Appl. No.: 856,188

[56] References Cited UNlTED STATES PATENTS 3,345,197 10/1967 Martini et a1 ..117/107.2 P 3,079,276 2/1963 Puyear et a1... ...117/107 2 P 2,957,782 10/1960 Boiler ..204/38 2,917,818 12/1959 Thomson... ...117/114C 2,894,884 7/1959 Gray ..204/38.3 2,611,163 9/1952 Schaefer et a1. ..204/3 8.3 1,637,033 7/1927 Basch .117/107.2 P 1,480,779 1/1924 Pacz ..148/6.35 1,881,064 10/1932 Sayles eta1.... .117/107.2 P 2,970,065 l/1961 Greene et al. ..l17/8 FOREIGN PATENTS OR APPLICATIONS 428,855 5/1935 Great Britain ..1 17/1072 P Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews AttorneyMcDougall, Hersh, Scott & Ladd [5 7] ABSTRACT The treatment of high nickel and cobalt base alloy to improve the corrosion resistance of parts formed thereof by first applying a coating of nickel and then subjecting the part to difiusion coating to aluminize the surface.

14 Claims, No Drawings METHOD FOR SURFACE TREATMENT OF NICKEL AND COBALT BASE ALLOYS This invention relates to the art of aluminizing metal surfaces by diffusion to provide a surface on the metal which is rendered more resistant to corrosion or oxidation at high temperatures and/or in corrosive atmospheres, such as exist in a combustion engine, turbine, and the like. By diffusion of aluminum into the surface of such metals as high nickel or cobalt alloys and high alloy steels, heat shock erosion, corrosion resistance and other physical and mechanical properties are markedly improved.

To the present, in the aluminizing treatment by diffusion coating, the metal part is heated to a temperature above 1000 C. in a pack formed of a powdered mixture of metallic aluminum and aluminum oxides, without and preferably with a small amount of halide salt such as ammonium chloride or ammonium fluoride, for about 4 to hours in a nonoxidizing atmosphere.

The aluminum diffuses into the surface, usually to a depth within the range of about 10-20 microns, depending somewhat upon the time and temperature of the aluminizing treatment and the amount of aluminum in the pack, with the amount of aluminum in the diffusion layer decreasing from the surface inwardly toward the center in amounts somewhat proportionate to the distance from the surface.

It is an object of this invention to provide an improved aluminized article and method for preparation of same wherein the diffusion coating of aluminum remains concentrated in a narrow layer on the surface of the article without excessive diffusion into the interior of the article; whereby a better bond is achieved between the diffusion coating and metal substrate; and whereby a complex series of compounds are formed in the diffusion layer to provide an improved coating which offers higher temperature corrosion resistance.

In accordance with the practice of this invention, the parts formed of a superalloy, and preferably nickel and cobalt based alloys, are first processed to provide the surface portions to be aluminized with a thin coating of nickel, in a first coating step. The coated parts are then packed in the conventional manner and conventional compositions for aluminizing the surface by diffusion transfer of aluminum. The presence of nickel as a precoat on the metal surface is believed to operate as a barrier coat which concentrates the diffused aluminum in the surface portions of the metal parts to provide an aluminized surface having greatly improved corrosion resistance, especially when measured at high temperature and in the presence of highly corrosive gases.

In the described two-stage process of first nickel plating and then diffusion coating to aluminize the plated surface by a pack cementation process it is desirable to deposit a nickel coating in the first stage having a thickness greater than 0.000] inch and preferably having a thickness within the range of0.000l to 0.001 inch.

The desired thickness of nickel coating can be deposited by conventional electroplating processes, such as described in the article published by the ASM Committee on Nickel Plating, entitled Nickel Plating, published in the Metals Handbook, Volume II, pages 432-443, under general purpose plating baths. Instead, the desired thickness of nickel coating can be deposited on the surface of the parts nonelectrically, as described on pages 443-445 of the Metals Handbook, Volume ll, supra, under theheading Nonelectrolytic Nickel Plating.

The aluminizing pack employed in the pack cementation process for aluminizing the nickel-coated surfaces can be formulated to contain aluminum metal in finely divided form in an amount within the range of 0.1 to 10 percent by weight with the remainder formed of a finely divided filler, preferably alumina. Although it is not essential, use can be made of an energizer, such as ammonium chloride or ammonium fluoride, in an amount within the range of 0.01 to 5 percent by weight of the pack. A hydrogen or inert atmosphere is maintained during diffusion coating while the materials are heated to a temperature within the"range of 1,800 to l,200 F. or a time sufficient to build up a final coating thickness within the range of 0.001 to 0.005 and preferably within the range of 0.00 l 5 to 0.003 inch. The desired coating thickness is obtained with a pack of the type described in about 9 to 10 hours of heating.

The following examples are given by way of illustration, but not by way of limitation, of the practice of this invention:

Alloy Composition:

Example 1 Percent by Weight Ni 70.0 Cr l2.0 W 5.0 Al 5.0 M0 3.5 Ti, Nb, 'la 2.5 Fe, C, Mn, Si Balance Example 2 Percent by Weight C0 60.0 Cr 20.0 W 10.0 Nb 2.0 Ni LO Fe, C, Mn, Si Balance Example 3 Percent by Weight C 0.08 Mn 0.75 Si 0.75 Cr |9.0 Co l9.5 M0 4.0 Ti 2.) Al 2.9 Fe 4.0 Ni Balance Example 4 Percent by Weight C 0. l 2 Mn 0. l5 Si 04 Cr I10 M0 4.5 Ti 06 Al 6.0 Fe L0 Cb 2.25

' Ni Balance First stage of nickel coating:

Example 5 Composition of Electrolytic Bath Nickel sulfate. NiSO GILO 30 to 55 Nickel chloride, NiCl,6H,O 4 to 8(a) Nickel sulfamate,

Ni so,NH, Nickel fluoborate,

K m Total nickel as metal 7.7 to [4.2 Boric acid, H BO 4 to 6 Antipitting additives (b) 3 4 Operatlng Conditions Operating Conditions pH 1.5 m 52 PH H5 Temperature, F. 190 to 210 Cullen dcnslly, Plating rate (approx). a. per sq. ft. to I00 5 mil pct Example 6 Example l0 l0 a Composition of Electrolytic Bath Pack:

5 pounds powdered aluminum metal Nickel sulfate 100 pounds powdered alumina NiSO,6H,0 Nickel chloride, Nicl,6li,o 0 m 4 Example 1 1 Nickel sulfamate, Ni(SO,NI-l,), 3s m 60 Nickel fluobora'e- 7 pounds powdered aluminum metal N'(BF4)= 100 pounds powdered alumina Total nickel as metal 8.2 to 15 01 Pound ammonium cmmidc Boric acid. M430 4 to 6 Antipitting additives (b) Operating C diti In the electrolytic plating systems of Examples 5 to 7, the part is suspended as a cathode in the electrolyte until a coating 2 F g thickness within the range of 0.0001 to 0.001 inch has been empemure. deposited. The part is then removed and rinsed with water to Current density, a. per sq. ft. 25 to 300 remove electrolytic.

EXample 7 In the nonelectrolytic systems of Examples 8 and 9, a thinner nickel coating is deposited on the metal surfaces. In practice, the parts are immersed in the bath with continuous C i i f El l i h movement until a nickel coating having a thickness within the range of 0.0001 to 0.001 inch is deposited and the part is then Nickel sulfate removed and rinsed. l The nickel plated parts are packed with the pack composi- Nlckel chlorlde, NiclzfiHzo 0 lo 2 non of Examples 10 and l 1 m a retort. The parts formed of the Nickel sulfamatc. cobalt alloy of Example 2 are heated in a hydrogen atft i m mosphere for 10 hours at 1950 F. while the parts formed of :12: 30 1 40 the nickel-based alloys of Examples 1, 3 and 4 are heated in a O 31 g g as mm M w 105 40 hydrogen atmosphere for 9 hours at l,950 F. to form parts Boric acid, a so, 2 to 4 having a final coating thickness withln the range of 0.0015 to Antipitting additives (b) inch.

Instead of making use of the nickel or cobalt based alloys of Operatmg Commons Examples 1 to 4, use can be made of parts formed of nickel or P" U m 4 cobalt based superalloys in which corrosion resistance at high Temperature, F 100 m 160 temperature and resistance to deterioration by the sulfides CUIICl'll density, present in corrosive gases is greatly improved. 25 The term powdered or finely divided" form, as applied to the elements in the pack composition, is meant to refer to Example 8 aluminum metal particles of preferably less than 5 microns and is meant to refer to particles of less than 100 microns and preferably within the range of 5-100 microns for the filler or alumina component of each pack. Composmon Nonelectmlyuc Bath 5 5 It will be understood that changes may be made in the c ch10 details of formulation and o eration without de artin from lck l n p p g (Nicl,eH,o so oz. P01 gal. the spirit of the invention, especially as defined in the follow- Boric acid (H3805) 4 oz. per gal. l i

0 c We claim:

pew mg on I Ions 1. A method for surface treatment to improve the corrosion PH 4,5 resistance of products having surface portions formed of a Temperature 160 F. metal selected from the group consisting of nickel base alloys,

cobalt base alloys, and superalloys, comprising the steps of ap- Example 9 plying a first coating of nickel on surfaces of the product, and then alumlnlzlng the nickel coated surfaces by dlffuslon transfer. 2. The method as claimed in claim 1 in which the first coat- Composmo" Nonelectl'olytlc Bath ing of nickel is applied in a coating thickness greater than Nickel chloride 30 00001 inch" Nickel sulfa: 7O 3. The method as claimed ln claim 1 ln Much the first coat- Sodium hypophosphite 3 l0 ing of nickel is applied by a nonelectrolytic system in a coating Sodium acetate thickness within the range of 0.0001 to 0.001 inch. f 4. The method as claimed in claim 1 m which the first coat- Sodlum succlnate d k h. h Lactic acid mg of nlckel ls app lle in a coatlng t lc ness wlt m t e range 75 of0.0001 to 0.001 inch.

Propionic acid 5. The method as claimed in claim 1 in which the nickel coating is applied by electroplating the product.

6. The method as claimed in claim 1 in which the nickel coating is deposited by chemical deposition.

7. The method as claimed in claim 1 in which the aluminizing coating is applied with the materials at elevated temperature.

8. The method as claimed in claim 7 in which the materials are applied at elevated temperature within the range of 1 ,800 to 2,000 F.

9. The method as claimed in claim 1 in which the aluminizing coating is applied in a nonoxidizing temperature.

10. The method as claimed in claim 1 in which the aluminizing coating is applied in an amount to provide an overall coating thickness within the range of 0.001 to 0.005 inch.

11. The method as claimed in claim I in which the aluminizing coating is applied in an amount to provide an overall coating thickness within the range of 0.0015 to 0.003 inch.

12. The method as claimed in claim 1 in which the product is aluminized by packing the nickel coated product in an aluminizing composition containing aluminum metal in finely divided form in an amount within the range of 0.l to l0 percent by weight uniformly distributed in a filler.

13. The method as claimed in claim 12 in which the tiller is alumina.

14. The method as claimed in claim 12 in which the aluminizing composition contains an energizer. 

2. The method as claimed in claim 1 in which the first coating of nickel is applied in a coating thickness greater than 0.0001 inch.
 3. The method as claimed in claim 1 in which the first coating of nickel is applied by a nonelectrolytic system in a coating thickness within the range of 0.0001 to 0.001 inch.
 4. The method as claimed in claim 1 in which the first coating of nickel is applied in a coating thickness within the range of 0.0001 to 0.001 inch.
 5. The method as claimed in claim 1 in which the nickel coating is applied by electroplating the product.
 6. The method as claimed in claim 1 in which the nickel coating is deposited by chemical deposition.
 7. The method as claimed in claim 1 in which the aluminizing coating is applied with the materials at elevated temperature.
 8. The method as claimed in claim 7 in which the materials are applied at elevated temperature within the range of 1,800* to 2, 000* F.
 9. The method as claimed in claim 1 in which the aluminizing coating is applied in a nonoxidizing atmosphere.
 10. The method as claimed in claim 1 in which the aluminizing coating is applied in an amount to provide an overall coating thickness within the range of 0.001 to 0.005 inch.
 11. The method as claimed in claim 1 in which the aluminizing coating is applied in an amount to provide an overall coating thickness within the range of 0.0015 to 0.003 inch.
 12. The method as claimed in claim 1 in which the product is aluminized by packing the nickel coated product in an aluminizing composition containing aluminum metal in finely divided form in an amount within the range of 0.1 to 10 percent by weight uniformly distributed in a filler.
 13. The method as claimed in claim 12 in which the filler is alumina.
 14. The method as claiMed in claim 12 in which the aluminizing composition contains an energizer. 